LeetCode-Java-404. Sum of Left Leaves

题目

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

代码

通过递归

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        int sum=0;
        //如果为null直接返回0
        if(root==null){
            return 0;
        }
        //如果左子树不为空
        if(root.left!=null){
            //判断此左子树是否子树
            if(root.left.left==null&&root.left.right==null){
                sum+=root.left.val;
            }else{
                //如果此左子树还拥有子树，继续向下
                sum+=sumOfLeftLeaves(root.left);
            }
        }
        //当左树判断完以后判断右树
        sum+=sumOfLeftLeaves(root.right);
        return sum;
    }
}